LITTLE ROCK (AP) — Republicans have made gains in Arkansas and may be on the verge of a historic takeover of the state Legislature after campaigning primarily on a vow to cut state spending and to never support any tax increases. A proposal going before voters next month to raise Arkansas' sales tax to pay for highway improvements is chipping away at some of that anti-tax sentiment among the state's top GOP officials.

Lt. Gov. Mark Darr, U.S. Sen. John Boozman and other GOP lawmakers have said they'll vote for a proposed constitutional amendment adding a half-cent sales tax to pay for highway improvements over the next decade. The support comes despite pledges by many of them to oppose tax increases.

It's a position that Republican supporters of the tax say they'd rather avoid.

"It wasn't something where I was like, 'well, I'm going to wake up today and as the highest elected Republican in the state back a tax,'" Darr told The Associated Press last week. "It's not something that I wanted to do, but I do think the people of Arkansas need to learn the facts and at the end of the day, make their own decision."

Though neither party has taken a position on the tax hike proposal, it's generally found more support among Democrats than Republicans. The state's top Democrats — Gov. Mike Beebe, Attorney General Dustin McDaniel, U.S. Sen. Mark Pryor and Congressman Mike Ross — support the measure.

The biggest obstacle in winning over Republicans is a no-tax pledge many from the party have signed. All of the Republican members of the state's congressional delegation and 17 GOP state legislators have signed pledges from the Washington-based Americans for Tax Reform to oppose tax increases.

The federal version of the group's pledge commits lawmakers to oppose any effort to increase marginal income tax rates and "any net reduction or elimination of deductions and credits, unless matched dollar for dollar by further reducing tax rates." State officials and legislators sign a pledge promising to oppose "any and all" efforts to increase taxes.

Some high-profile Republicans who have signed no-tax pledges have opted out of the public debate altogether. U.S. Rep. Rick Crawford, Secretary of State Mark Martin and U.S. Rep. Steve Womack all declined to say through spokespeople whether they'd vote for the hike.

The amendment calls for the authorization of $1.3 billion in bonds to fund highway projects. Those bonds would be paid for by a half-cent sales-tax increase that, if approved, would increase Arkansas' state sales tax to 6.5 percent from 6 percent. The tax would end when the bonds are paid off, which is expected to take no more than 10 years.

Rep. Jonathan Barnett, a Republican who sponsored legislation referring the tax hike to voters, said the tax pledge and potentially close legislative contests around the state have been obstacles in winning over some GOP support. Barnett, a former highway commissioner, has not signed the no-tax pledge.

"There are obviously a lot of Republicans who support it. Some others are having to be cautious," Barnett said.

It's a dilemma many Republicans who swore to oppose tax increases faced last year, when the Legislature voted to put the measure on the ballot. Many said they didn't consider supporting the legislation a violation, since they were merely referring an increase to voters. Darr said he doesn't think his support runs afoul of the ATR pledge, since he didn't vote for the measure in the Legislature.

"Mathematically, it's more detrimental if we don't do this program and not do anything," Darr said.

Boozman said his vote for the amendment next month doesn't violate his promise either, since he's casting it as a private citizen and not on any legislation before the U.S. Senate.

"I think it's a very good thing that, rather than cramming a tax down the people's throat, they're allowed to determine for themselves whether it's worthwhile and whether they'd like to contribute the money," Boozman said. "I think it's a really good model."

It's unclear whether any of the Republicans publicly backing the tax hike will face a backlash from the same voters who elected them partly on their no-tax vows. Darr is considering a run for governor in 2014, and Boozman isn't up for re-election until 2016.

Many of the Republicans who oppose the tax say they're not campaigning actively against the proposal, and no group has registered with the Ethics Commission to oppose the ballot measure.

Rep. David Sanders, a Republican who is running for a state Senate seat, voted against referring the tax to voters and said he plans on casting his ballot against the increase next month. Sanders said he thinks the focus should be on alternative to tax hikes, such as diverting tax revenue from road-related products to highways.

"I think for years the problem in Arkansas has been when there is a problem or a need, the politicians always have defaulted to raise taxes," Sanders said. "I ran on stopping that."

U.S. Rep. Tim Griffin, who's considered a potential candidate for governor or the Senate in 2014, said he's also personally opposed to the tax hike. Griffin said in a statement that the Legislature should "make highway funding a higher priority than it is now by reforming state government and making highway funding a permanent component of the state budget paid for with general revenue tax dollars already collected."

Sen. Michael Lamoureux, R-Russellville, likewise opposes the tax hike but said he thinks there's enough room in the party for different opinions on an issue that lawmakers have grappled with for years with solutions that don't please everyone.

"It's not really that anybody is excited about dealing with this," he said.